Numerical and analytical model of the inclined impact of a droplet on a solid surface in a thermal spray coating process

In this paper, the inclined impact of a droplet on a solid surface in a spray coating process is studied using both numerical and analytical models. The numerical simulation is based on a previously developed model that includes the solution of Navier-Stokes equations along with an equation for the liquid free surface. The contact angle is modeled using two advancing and receding angles at the liquid front on the solid surface. The close agreement between the results of the numerical model with those of the experiments shows that the model can accurately predict the droplet impact behavior. Using the balance of droplet energy before and after the impact, a simple analytical model is presented for the maximum spread of a droplet during an inclined impact. This model is an extension of a previously developed model for the normal impact of a droplet on a solid surface. A comparison between the results of the analytical model with those of the simulations and experiments verifies the accuracy of the analytical model predictions for the maximum spread of a droplet in a spray coating process. Based on the analytical model, for high Reynolds numbers and small angles of impact, the effect of Weber number on the maximum spread is increased. For low Reynolds numbers and impact angles close to 90o, the maximum spread remains nearly constant